Journal of Datta Meghe Institute of Medical Sciences University

: 2019  |  Volume : 14  |  Issue : 3  |  Page : 166--170

Comparative Evaluation of 5th- and 7th-Generation Bonding Agents: An In vitro Study

Madhu Varma, Shweta Sedani, Pradnya Nikhade 
 Department of Conservative Dentistry and Endodontics, Sharad Pawar Dental College and Hospital, DMIMS (Deemed to be University), Wardha, Maharashtra, India

Correspondence Address:
Prof. Madhu Varma
202, Gokul park1, In Front of Kachore Lawns, Near Rakshak Mart, Besa Belatarodi Road, Manish Nagar, Nagpur - 440 015, Maharashtra


Objective: The purpose of this study is to evaluate microleakage in 5th- and 7th-generation bonding agents. Materials and Methodology: A total of thirty recently extracted human premolars were subjected to this study. Class V cavity preparations were made on the lingual and buccal surfaces of extracted premolars. Occlusal margins were made in enamel and gingival margin in cementum/dentin. The teeth were divided into two groups of 15 each and 30 cavity preparation per group. The groups were treated with Single Bond 2 and Single Bond Universal as dentin-bonding agents. The prepared cavity was restored with resin composite (Clearfil APX) after the application of bonding agents. The specimens were thermocycled and stained with 2% methylene blue dye and were section for the evaluation of dye penetration. Data were analyzed using one-way analysis of variance test and Dunn's procedure for pairwise comparison of data. Results: This study showed that the preparations treated with Single Bond Universal showed less microleakage than Single Bond 2, and it had a better marginal sealing ability at enamel margins better than dentin. Interpretation and Conclusion: This study demonstrated that Single Bond Universal had a better sealing capacity at both coronal (enamel) and apical (dentin/cementum) margins compared with Single Bond 2 agent used.

How to cite this article:
Varma M, Sedani S, Nikhade P. Comparative Evaluation of 5th- and 7th-Generation Bonding Agents: An In vitro Study.J Datta Meghe Inst Med Sci Univ 2019;14:166-170

How to cite this URL:
Varma M, Sedani S, Nikhade P. Comparative Evaluation of 5th- and 7th-Generation Bonding Agents: An In vitro Study. J Datta Meghe Inst Med Sci Univ [serial online] 2019 [cited 2020 Aug 4 ];14:166-170
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The conventional acid-etch technique was pioneered by Bounocore[1] for composite resin restorations. It is one of the major threats to the long-term achievement of resin restorations. “The passage of bacteria, fluids, molecules, or ions between the wall of the cavity and the restorative material is called microleakage.“[2]

Clinical conditions such as sensitivity, recurrent caries, discolored restorative margins, pulpal damage, and breakdown of the restorative material are present in association with microleakage. Therefore, when developing an adhesive system for dental restorative applications, prevention of microleakage is the most important consideration.

Currently, popular adhesive systems were total etch technique (“4th” generation) designed with three separate steps in the bonding process: etching, priming, and bonding. To provide greater bond strength, sealing of tissue permeability, convenience and ease of application, and development of other adhesives have been done. Adhesives used today are the “5th generation” in which the primer and adhesive are combined in a single bottle, but a prebonding step of total acid etching is still needed to be done. These systems have been proved to be effective in preventing microleakage in many studies. Self-etching primer systems (“6th generation“) have also been developed which has primer and etchant in single bottle, eliminating separate rinsing and drying steps, but require a separate application of an adhesive resin or bonding agent. More recently, “7th generation” adhesive systems have been introduced; in this, etchant, primer, and bonding agent have been incorporated into a single bottle and are designed to release fluoride and changes color on the completion of polymerization.

While many studies have investigated the bond strength and marginal adaptation of self-etching primers, many compared the microleakage and interface morphology at the margins of restorations placed using these systems. However, other studies have reported that separate etching, priming, and bonding steps are more effective in the reduction of microleakage. There is, therefore, a need to study the microleakage of specific adhesive systems with significant formulation.

The main purpose of the present study was to compare the microleakage in restored teeth using 5th generation adhesive ( Single Bond 2 adhesive 3M ESPE Adper (St. Paul, MN 55144 USA)) with 7th generation adhesive ( Single Bond Universal 3M ESPE (Heraeus Kulzer D-63450, Hanau, Germany)).

 Materials and Methodology

This study was conducted in Sharad Pawar Dental College and Hospital, Sawangi (Meghe), Wardha after obtaining ethical clearance from the institutional ethical committee.

Thirty recently extracted, noncarious, unrestored teeth were collected, which were extracted due to orthodontic reasons. Scraping of residual tissue tags from the teeth was carried out, and teeth were kept in 2.6% sodium hypochlorite solution and rinsed under running water for 15 min.

Class V cavity on facial and lingual surfaces of each tooth was prepared with a cylindrical diamond bur. The dimension of the cavity was approximately 3-mm wide mesiodistally parallel to cementoenamel junction (CEJ), 2-mm wide occlusogingivally, and 1.5-mm deep approximately. Gingival half of the preparation was extended 1 mm below the CEJ.

Group I: Fifteen teeth (thirty cavity preparations) – the 5th generation bonding agent Single Bond 2 (3M ESPE Adper) was usedGroup II: Fifteen teeth (thirty cavity preparations) – the 7th generation bonding agent Single Bond Universal (3M ESPE) was used.

Manufacturer's instructions were applied while using bonding agents, and the cavities were restored with resin composite (Clearfil APX).

All the teeth were subjected to water baths of 5°C ± 2°C and 55°C ± 2°C, with 500 thermal cycles with a dwell time of 15 s. Dye-leakage test was performed. Two coats of nail varnish were applied to within 1 mm of the tooth-restoration margin. Root apices were covered with modeling wax, and specimens were kept in methylene blue solution for 24 h at 37°C.

Radicular parts of the teeth were cut 4–5 mm below the CEJ after staining and rinsing the teeth. The coronal parts were sectioned mesiodistally and then buccolingually in the approximate center of the restoration with a low-speed diamond saw. Stereomicroscope at original magnification (×16) was used to assess microleakage for both occlusal (enamel) and cervical (cementum) margins.

The depth of the dye leakage was assessed according to the following scale:

0 – No penetration of dye1 – Penetration of dye up to one-third of the cavity2 – Penetration of dye up to two-third of the cavity3 – Penetration of dye up to full-cavity depth4 – Penetration of dye onto the axial wall of the cavity preparation.

A nonparametric analysis of variance test was used to calculate significant differences among the groups. Pairwise comparisons between groups were made using Dunn's procedure for nonparametric data. Occlusal and gingival margins within the sample groups were compared using the Wilcoxon signed-rank test. The level of significance was established as P < 0.05 for all tests.


[Table 1] shows grades of dye penetration into coronal (enamel) margins.{Table 1}

[Table 2] shows grades of dye penetration into apical (cementum/dentin) margins.{Table 2}

[Table 3] shows that the mean value of 5th generation is 2.06 ± 1.16 and the mean value of 7th generation bonding agent is 1.14 ± 1.06, but there is no significant difference in microleakage of 5th and 7th generation bonding agents, when compared to enamel (P = 1.000).{Table 3}

[Table 4] shows the mean value of 5th generation bonding agent (2.20 ± 1.12) and the mean value of 7th generation bonding agent (1.33 ± 1.11), but when we compare the microleakage of 5th generation bonding agent with 7th generation bonding agent at cementum level, it comes out (P = 0.564), which is nonsignificant.{Table 4}

“The results showed that the 7th generation bonding system showed less microleakage as compared to 5th generation bonding agents at both coronal and apical margins more effectively.“


The concept of bonding restorative materials to tooth structures was long before the advent of composites.[3] Major drawbacks of these adhesives were higher placement complexity and technique sensitivity.[4] Enamel adhesion is a predictable and established entity; bonding to dentine is more difficult to achieve. To overcome this challenge, technological advancements of dentine bonding agent have, at this time, developed into two trends: total acid-etching techniques (5th generation adhesives) and self-etching primer technique (6th and 7th generation adhesives).[5]

Self-etch adhesives composed of aqueous mixture of acidic functional monomers which are phosphoric acid esters, which does not need a separate acid-etch component and subsequent rinsing procedures. Self-etch system also purportedly increases the marginal integrity and thus reduces or eliminates patient's symptoms.[4]

The results showed that at the coronal (enamel) margins of the cavity, 7th generation adhesives showed less microleakage, whereas 5th generation adhesive showed significantly greater microleakage at the coronal margins.

The explanations for these results of Single Bond 2 include (5th generation dentin-bonding agent [DBA]):

Single bond shows the functions of the primer and adhesive components of the conventional three-step adhesive system and has alcohol and water as solvents in its compositionThe presence of alcohol in the adhesive enhances the diffusion into the dentin, thereby promoting adhesion. The moisture of dentin tubules pulls the alcohol and resin into and in between the tubules. The alcohol and moisture then vaporize from the substrate and resin left behind.[6]

The explanations for these results of Single Bond Universal include (7th generation DBA)

The 7th generation has the acid, primer, and resin in one bottle, which reduces separate etching, rinsing, and mixing for the light-cured productsHigh bond strength (20–30 MPa) to enamel and dentin. Ensuring complete seating of restorations by thin film thickness and fluoride releasing to prevent secondary caries7th generation bonding agent bonds to the smear layer as a bonding substrate. The acidic primer demineralizes the smear layer and the top layer of the underlying dentin surface. The acidic primer also infiltrates the exposed collagen with hydrophilic monomers, which then copolymerize. Because of not rinsing the etched surface, the demineralized smear layer is incorporated into the hybrid layer. The hybrid layer ranges in thickness from 0.5 μm to 5 μmAfter the primer decalcifies the inorganic content in dentin, the acidic primer and adhesive monomers also infiltrate collagen fibers to the same depth, which should decrease voids, potential leakage, and postoperative sensitivity.

None of the groups of the DBAs prevented the microleakage completely at the restoration–tooth interface.[3],[7],[8] The results also showed that at the apical (dentin/cementum) margins of the cavity, Single Bond Universal (7th generation adhesive) exhibited less microleakage. Single Bond 2 (5th generation adhesive) showed significantly more microleakage at the apical margins.

The results also suggest that the microleakage at the enamel margins is less compared to that of the microleakage at the dentin/cementum margins.[1],[9] These results were in relation to the previous results.[1],[4] The most acceptable reasons for the less microleakage at the enamel margins compared to that of the microleakage at the dentin/cementum margins are:

The hypermineralization of the dentin surface and subsequent collapse of the collagen fibrillar network, configuration of cavity (C factor), orientation of dentinal tubule to the cervical wall (CEJ), organic content of dentin substrate and movement of dentinal tubular fluids, for proper demineralization and hybrid layer formation, incomplete removal of the smear layer by acidic primers, and ineffective infiltration/penetration of primer components into the demineralized collagen fibrillar network. Solvent carriers such as water, alcohol, and acetone in the adhesive agent reacted differently with varying degrees of surface moisture which was present in the tubules.[7] In class V cavities, located at approximately 1 mm from the CEJ, dentinal tubules are oriented parallel to the cervical wall. A classic hybrid layer formation is not seen in the dentinal margins, and this absence is an important reason of leakage.[1]

Microleakage tests provide adequate screening methods, for determining clinical achievement and longevity of the adhesive systems. Although this study was conducted in vitro, this can be a screening apparatus for showingin vivo studies. Previous research proves that data obtained fromin vitro microleakage testing may be useful but not always necessarily reproducible in clinicalin vivo conditions.[10]

The results of this study demonstrate that the nature of the dentinal morphology is an important factor and an unconquerable hindrance for perfect adhesion of restorative materials to the tooth structure. Clinical trials should be performed for carious and noncarious Class V cervical lesions to assess the performance of these new adhesive systems before definite conclusions can be made [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9].{Figure 1}{Figure 2}{Figure 3}{Figure 4}{Figure 5}{Figure 6}{Figure 7}{Figure 8}{Figure 9}


Although it is desirable from a clinician's point of view to reduce the number of steps involved in adhesive bonding procedures, the adverse effects of reducing individual steps need to be carefully considered. One-step bonding formulations are more chemically aggressive, excessively hydrophilic, and low viscosity formulations for concurrent etching, priming, and bonding effects. 5th generation bonding systems, which use two steps (self-etching primer and adhesive), are good alternatives to total-etch three-step (etch, prime, and bond) adhesive systems. 7th generation bonding systems are more effective in preventing microleakage but low viscosity, low PH, and high hydrophilicity of this adhesive may adversely affect its ability to seal the dentin-adhesive interface effectively.[11],[12],[13],[14].

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest .


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